As happy, simple, sweet, etc. as can be
Definition 1 of 1
Pro Tip 1/3Maximum Expression
Highlights the highest degree of a quality, suggesting nothing could be more so. 
She is as happy as can be with her new job.
Pro Tip 2/3Emotional Accent
Often accentuates strong emotions or states of being, conveying a deep level of feeling. 
After the concert, the fans were as excited as can be.
Pro Tip 3/3Contrasting Context
Works well in contexts where a contrast is being made between expectations and reality. 
Despite the noisy street, her room was as peaceful as can be.